1. Field of the Invention
This invention relates to the preparation of high precision alloy, and in particular, high-strength nickel-based amorphous compositions for fabrication of glass-coated microwires.
2. Description of the Related Art
It has been the tendency in modern technologies to demand new materials and processes for their production from material engineering. Strengthening of the structural materials by reinforcing them with high strength fibers or wires is one of the problems of the material engineering in the production of elements and structures operating under harsh environment and exploitation conditions.
The modern methods for strengthening of metals and alloys employ various treatments, e.g., strain hardening, thermal and thermal-mechanical treatment, precipitation hardening, martensite reinforcement, etc. Such treatments allow to obtain, for example, steels and alloys having tensile strength in the range of 1000–3000 MPa. In particular, the forming in the metal matrix such strengthening phases as δ-phase (Ni—Mo), σ-phase and ρ-phase (Cr18Mo42Ni40) has a great potential for obtaining high strength materials.
Known techniques for casting microwires in glass insulation enable to form an amorphous homogeneous structure and the strengthening phases in the material, and thereby increase the strength characteristic up to 3000–4500 MPa. The high strength is, inter alia, attained by providing a high degree of the melt oversaturation by applying reinforcing components and “freezing” the alloy in this condition at quenching the material from the liquid phase with the cooling rate of up to 3×106 K/s.
According to the microwire casting techniques, a glass tubing containing the desired metal batch is heated to a temperature sufficient to melt the metal and soften the glass. In general, the heating is obtained via electromagnetic induction for melting the metal which, in turn, softens the glass. The outer glass shell is then drawn out as fine as desired. As a result, two coaxial flows arise: one of the melted metal in the center and another of softened glass around the metal one. After leaving the heating zone, both flows pass through a water stream, for cooling and solidifying. The result is a continuous microwire with the metal being continuously cast as a core covered with a glass coating.
U.S. Pat. No. 6,325,868 discloses a nickel-based amorphous alloy having a superior amorphous phase-forming ability. This alloy contains nickel, zirconium and titanium as main constituent elements along with additional elements, such as Si or P. Also, at least one kind of element selected from the group consisting of V, Cr, Mn, Cu, Co, W, Sn, Mo, Y, C, B, P, Al can be added to the alloy composition in the range of content of 2 to 15 atomic %.
One of the drawbacks of this alloy is that it contains a rather large amount of such elements as Ti and Zr, i.e., from 40 to 60%, which are easy oxidizable metals. In this case the alloy drop can turn into oxide during the microwire casting process and prevent microwire manufacture.
U.S. Pat. No. 4,668,310 discloses amorphous alloys having high strength and hardness. The general composition formula of these alloys is TaXbZcMd, where
T is at least one of Fe, Co and Ni;
X is at least one of Zr, Ti, Hf and Y;
Z is at least one of B, C, Si, Al, Ge, Bi, S, P;
M is at least one of Mo, Cr, W, V, Nb, Ta, Cu, Mn, Zn, Sb, Sn, Be, Mg, Pd, Pt, Ru, Os, Rh, Ir, Ce, La, Pr, Nd, Sm, Eu, Gd, Th, Dy; and
a is 70–98 atomic %,
b is from 5 to 30 atomic %,
c is from 0 to 0.5 atomic %, and
d is not more than 20 atomic %,
and sum of a, b, c, and d is 100 atomic %.
One of the disadvantages of this alloy is in the fact that it is not suitable for microwire casting, owing to the deficiency of such elements as B and Si (less than 0.5%). For such contents of B and Si, the wetting ability of silica-boride glasses by the metal melt is not sufficient for providing a mass microwire manufacturing process. Moreover, the content of such elements as Cr and Mo does not exceed 20%, that prevents from forming the high strength ρ-phase.
USSR inventor's certificate No. 428,028 discloses an alloy for casting of the microwire. This alloy was developed by taking into account the specific conditions of physical and chemical interaction between the metal melt and glass during microwire casting process. Alloy has the following content, by weight %:
Cr: 10.0–20.0%,
Mo: 25.0–40.0%,
Si: 0.2–3.0%,
B: 0.1–1.2%,
Ni: the base.
The tensile strength of a microwire obtained from this alloy is between 3000 and 4500 MPa.
One of the disadvantages of utilization of this alloy is that it is not suitable for preparing long continuous microwire lines (more than 100 m) during the microwire casting process. Moreover, the obtained microwire has a large dispersal of diameter along its length (up to +/−20%). These drawbacks are associated, inter alia, with insufficient purification of the alloy mainly from entrapped gas and other non-metallic inclusions. These disadvantages limit and sometime even restrict practical utilization of the microwires obtained from this alloy, especially when the strengthening of structure is achieved as a result of the winding of the reinforced microwire. Likewise, due to the lack of an amorphizer in the alloy composition, an amorphous structure of the alloy cannot be achieved, that prevents from obtaining an amorphous homogeneous alloy.
USSR inventor's certificate No. 662611 discloses an alloy having the following composition, by weight %:
Cr: 18–40%,
Mo: 30–40%,
Si: 0.2–3.0%,
B: 0.1–1.2%,
Zr: 0.3–1.0%,
Ni: the base.
The main disadvantage of this alloy, as well as in the above case, is the impossibility of fabrication of the microwire having long continuous length and small dispersal of the wire's diameter along its length. Notwithstanding the alloy composition includes such effective amorphizer as Zr, it is still difficult to provide the amorphous structure, because the amorphization for such alloy can be only achieved when the content of Zr is not less than 1.2%.